Apolipoprotein-CIII (apo-CIII) is involved in triglyceride-rich lipoprotein metabolism and linked to beta-cell damage, insulin resistance, and cardiovascular disease. Apo-CIII exists in four main... Show moreApolipoprotein-CIII (apo-CIII) is involved in triglyceride-rich lipoprotein metabolism and linked to beta-cell damage, insulin resistance, and cardiovascular disease. Apo-CIII exists in four main proteoforms: non-glycosylated (apo-CIII0a), and glycosylated apo-CIII with zero, one, or two sialic acids (apo-CIII0c, apo-CIII1 and apo-CIII2). Our objective is to determine how apo-CIII glycosylation affects lipid traits and type 2 diabetes prevalence, and to investigate the genetic basis of these relations with a genome-wide association study (GWAS) on apo-CIII glycosylation. We conducted GWAS on the four apo-CIII proteoforms in the DiaGene study in people with and without type 2 diabetes (n = 2318). We investigated the relations of the identified genetic loci and apo-CIII glycosylation with lipids and type 2 diabetes. The associations of the genetic variants with lipids were replicated in the Diabetes Care System (n = 5409). Rs4846913-A, in the GALNT2-gene, was associated with decreased apo-CIII0a. This variant was associated with increased high-density lipoprotein cholesterol and decreased triglycerides, while high apo-CIII0a was associated with raised high-density lipoprotein-cholesterol and triglycerides. Rs67086575-G, located in the IFT172-gene, was associated with decreased apo-CIII2 and with hypertriglyceridemia. In line, apo-CIII2 was associated with low triglycerides. On a genome-wide scale, we confirmed that the GALNT2-gene plays a major role i O-glycosylation of apolipoprotein-CIII, with subsequent associations with lipid parameters. We newly identified the IFT172/NRBP1 region, in the literature previously associated with hypertriglyceridemia, as involved in apolipoprotein-CIII sialylation and hypertriglyceridemia. These results link genomics, glycosylation, and lipid metabolism, and represent a key step towards unravelling the importance of O-glycosylation in health and disease. Show less
Prevention of hypertriglyceridemia is one of the biomedical targets in Glycogen Storage Disease type Ia (GSD Ia) patients, yet it is unclear how hypoglycemia links to plasma triglyceride (TG)... Show morePrevention of hypertriglyceridemia is one of the biomedical targets in Glycogen Storage Disease type Ia (GSD Ia) patients, yet it is unclear how hypoglycemia links to plasma triglyceride (TG) levels. We analyzed whole-body TG metabolism in normoglycemic (fed) and hypoglycemic (fasted) hepatocyte-specific glucose-6-phosphatase deficient (L-G6pc(-/-)) mice. De novo fatty acid synthesis contributed substantially to hepatic TG accumulation in normoglycemic L-G6pc(-/-) mice. In hypoglycemic conditions, enhanced adipose tissue lipolysis was the main driver of liver steatosis, supported by elevated free fatty acid concentrations in GSD Ia mice and GSD Ia patients. Plasma very-low-density lipoprotein (VLDL) levels were increased in GSD Ia patients and in normoglycemic L-G6pc(-/-) mice, and further elevated in hypoglycemic L-G6pc(-/-) mice. VLDL-TG secretion rates were doubled in normo- and hypoglycemic L-G6pc(-/-) mice, while VLDL-TG catabolism was selectively inhibited in hypoglycemic L-G6pc(-/-) mice. In conclusion, fasting-induced hypoglycemia in L-G6pc(-/-) mice promotes adipose tissue lipolysis and arrests VLDL catabolism. This mechanism likely contributes to aggravated liver steatosis and dyslipidemia in GSD Ia patients with poor glycemic control and may explain clinical heterogeneity in hypertriglyceridemia between GSD Ia patients. Show less
Hoekstra, M.; Sluis, R.J. van der; Hildebrand, R.B.; Lammers, B.; Zhao, Y.; Pratico, D.; ... ; Eck, M. van 2020
Objective:We tested the hypothesis that enlarged, dysfunctional HDL (high-density lipoprotein) particles contribute to the augmented atherosclerosis susceptibility associated with SR-BI (scavenger... Show moreObjective:We tested the hypothesis that enlarged, dysfunctional HDL (high-density lipoprotein) particles contribute to the augmented atherosclerosis susceptibility associated with SR-BI (scavenger receptor BI) deficiency in mice.Approach and Results:We eliminated the ability of HDL particles to fully mature by targeting PLTP (phospholipid transfer protein) functionality. Particle size of the HDL population was almost fully normalized in male and female SR-BIxPLTP double knockout mice. In contrast, the plasma unesterified cholesterol to cholesteryl ester ratio remained elevated. The PLTP deficiency-induced reduction in HDL size in SR-BI knockout mice resulted in a normalized aortic tissue oxidative stress status on Western-type diet. Atherosclerosis susceptibility was-however-only partially reversed in double knockout mice, which can likely be attributed to the fact that they developed a metabolic syndrome-like phenotype characterized by obesity, hypertriglyceridemia, and a reduced glucose tolerance. Mechanistic studies in chow diet-fed mice revealed that the diminished glucose tolerance was probably secondary to the exaggerated postprandial triglyceride response. The absence of PLTP did not affect LPL (lipoprotein lipase)-mediated triglyceride lipolysis but rather modified the ability of VLDL (very low-density lipoprotein)/chylomicron remnants to be cleared from the circulation by the liver through receptors other than SR-BI. As a result, livers of double knockout mice only cleared 26% of the fractional dose of [C-14]cholesteryl oleate after intravenous VLDL-like particle injection.Conclusions:We have shown that disruption of PLTP-mediated HDL maturation reduces SR-BI deficiency-driven atherosclerosis susceptibility in mice despite the induction of proatherogenic metabolic complications in the double knockout mice. Show less
